The mechanisms of action of two microbial enzymes involved in alicyclic ring metabolism will be studied from a stereochemical point of view. Cyclohexanone oxygenase is a flavoprotein which catalyzes a microbiological version of the Baeyer-Villager reaction, transforming cyclic ketones into lactones with the aid of molecular oxygen. The enzyme has been isolated and characterized; however its mechanism of action is still a matter of much speculation, as is true for most flavin-requiring enzymes. Cyclopropane carboxylate hydrolase catalyzes the hydrolytic ring cleavage of the carnitine derivative of cyclopropane carboxylic acid, ultimately affording 4-hydroxybutyric acid. The enzyme has not been purified, and very little is known regarding its mechanism of action. It is proposed to study the mechanisms of both enzymes through investigation of the stereochemical relationships between substrates and products. Involved will be (a) synthesis of substrates regio- and stereospecifically labeled with tritium, and (b) chemical degradation and enzymic analysis of chirally-labeled products. The pharmaceutical and environmental significance of the study of such catabolic processes is discussed.